Mechanical Rail Accelerator - Non-electromagnet "rail" gun

There's been all sorts of coil guns and rail guns being posted... but here's an interesting alternative. Not really useful, but amusing and effictive as a physics demo. The concept? Conservation of momentum

You'll need some magnets -preferably of the same size, type and somewhat strong (weak magnets do not work as effectivly). You're also going to need some ball bearings that show visible reactions in magnetic fields (aka nickel, coblat and iron/ferrous steel).

You're also going to need a ruler or some sort of straight edge. Movie on next step ;)

Step 1: Setup and Demonstration

I'm using the magnets found inside the magnetix brand of magnetic toy.

Place one magnet on one ball - then place the ball on your straight edge. Attach to the ball (but not to the magnet), one or two additional balls. You can stop here - or repeat this as many times as you want/can.

Take a different ball - and roll it towards the magnet on the first collection of magnet/balls. You should notice that once the ball is inside the magnetic field, it accelerates towards the magnet and makes contact with the magnet/ball cluster. Once contact is made, the last ball(s) separate in the same direction as the original ball.

This phenomina demonstrates the concept of conservation of momentum. If you were to repeat this demonstration without the magnets, you will have the same results with less motion.

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The rest of this instructable has more information/examples for those that want to know more.

Comments

[Crash2108]

Could this be turned into some sort of perpetual motion machine? Doubtful seeing depressing new-age thermodynamic laws. What changes would need to be implemented to keep this going in a loop?

[Dr KAZ]

Perpetual motion does not exist. Imagine a long track of the magnets/ball bearings arranged in a circular pattern. Consider an unfired pair of bearings as the ground state, then fire and you will see that the ground states activated by the processs of firing cannot fall back on their own to their original ground state where the loop is tied up. Undo this by adding more bearings? You might get lucky and have the thing run a few loops (might = no chance). You will always end up having an activated state (taken up energy, none to release), that has to give energy to activate something which is already in its activated state and that cannot fall back without energy input. Dead end. Just began typing this response, then scrolled down to see the rest... Sorry, could go on at length with the answer... The only (almost) perpetual machines around are atoms, but then again, they are not machines: their electrons keep spinning (rather, existing) around the nucleus for (an estimated) 1x10^30 years. That's (almost) perpetual (and useful) because it keeps my body intact and prevents me from becoming a black hole, which reminds me of a very nice Gary Larson cartoon...

[Attmos]

what about the earth around the sun, or the moon around the earth? perpetual motion?

[trebuchet03]

Newton's Laws of motion explain fairly well... Earth is sufficiently far away and of significant mass that small forces are nearly insignificant on Earth'y orbit. Comets, however, make up for a lack of mass with velocity which is why they can have open orbits and escape the sun.

The moon, on the other hand, is slowly being pushed away from Earth. About 4cm per year resulting in Earth's rotation slowing about 2 seconds every 100,000 years due to tidal forces and tidal locking (same reason we only see one side of the moon).

Satellites experience significant orbital decay as their mass is much smaller compared to Earth's mass and their distance is EXTREMELY close. Small forces due to atmospheric particles have large consequences over time.

The Earth, Sun and Moon are in motion, but their motion is not perpetual.

[Attmos]

we're way off topic about your rail gun, which is a cool display of physics by the way, and i'm sorry for this, lol. I get and agree with the moon thing, I'm not so conviced about the earth around the sun. newtons first law says, well you know what it says. there is no fluctuation or transfer of energy, just a perfect balance between gravity and centripetal force. is that not perpetual? lol, i'm really sorry, these things just eat at me until i get an answer i can understand. what do you think?

[trebuchet03]

Balanced forces does not necessarily mean perpetual. They just mean forces are balanced.

The Earth happens to be travelling through a vacuum - there really isn't much that will slow it down but things do. Meteorite strikes, technically, are forces on Earth. Earth has several orders of magnitude more mass - this is like throwing a grain of sand at a cannon ball. Sure, the grain of sand applies a force, but it's imperceptible.   Other than meteors, nearby asteroids and other celestial bodies will exert nonzero gravitational forces - Earth is still much larger - so large that it's irrelevant here...

To note: Earth is slowly moving away from the Sun - about 15cm per year. Slowly, we're stealing angular momentum from the Sun so that we may move into a higher orbit. On a human scale, this orbit is forever and perpetual. For the rate at which this occurs, the Earth will be swallowed by the Sun long before there's any orbit issue.

[Attmos]

cool. well thanks for indulging me. it's fun for me to learn about stuff like this and to be able to ask a few questions. the science channel doesn't do a good job of answering when i talk to it, lol.

[GASSYPOOTS]

also if you had a "prepetual waterwheel machine" it would stop because of friction from the wheel turning

[smb64]

 not unless you use a portals gun and have the track on a ramp.  : )

[taco_guy93]

Make this http://www.instructables.com/id/Make-a-magnet-sculpture/
put in a vacuum and push it and see how long the pendulum moves!

[crankyjew]

arent perpetual motion machines... erm... impossible??

[ARVash]

Pure perpetual motion machines .. . are, unless in a perfect universe, which .. we are not in :P. Near perpetual motion machines on the otherhand are quite possible. :P, Meaning they go for a REALLY long time, but technically, not forever ;P.

[chloride]

yea because some of the energy is given of as heat upon collision

[Crash2108]

Just don't have it collide. Suspend whatever machine with magnets instead of ball bearings and have it in a vacuum.

[bujo0]

still will lose energy to fiction from the balls on the track, and its very difficult to get a perfect vacum on earth, unless you mounds of money.

[lbrewer42]

Not really - many politicians achieve this state between their ears ;))

[freakyqwerty]

XD

[ARVash]

right, and then the only perfect vacuum on earth will be your wallet.

[_soapy_]

You will also lose energy to the magnetic material - the magnetic material uses a tiny amount of energy to flip it's magnetic domains about, every time the magnetic field reverses. This adds up with a lot of time. Also, you will get effects like friction in the string or track which will kill the motion fairly quickly, even in a vacuum.

[mikemmcmeans]

friction from the track would kill everything

[That Hurt This Time]

woohoo its a conspiracy!

[trebuchet03]

ahh this question... the quick answer is no. Every time the ball impacts, you loose some energy. Not to mention, the setup in this is vital - you want balls making contact with magnets, not with other balls. So eventually, the whole thing fizzles out - even in a straight line (assuming all magnets are about equal). Check out the link that crawler posted - that person explains it with a bit more detail. For testing how much energy is lost on impact, they suggest putting a ball in a tube -- then dropping another ball on top from a measured distance. If say you drop from 6 inches and it only bounces back up 2 inches that is a 66.6% loss of energy.

[Rectifier]

Not quite right. In a straight line, it WILL continue indefinately for as many stages as you have set up. Each stage contains X joules of energy that you put in it when you set it up in the initial state. When the stage fires, it adds:

Initial kinetic energy of ball from last stage + X joules stored in current stage - friction losses = more kinetic energy transferred to ball exiting stage

thus sustaining the reaction for an infinate number of stages in a row. What will eventually fizzle out is the acceleration, as it reaches a steady state. After a point, the same X joules added by the stage will be required to overcome the increased friction forces, and all successive stages will fire at a constant velocity. However, they will STILL FIRE in a line of stages that extends to infinity.
Assuming no friction and infinately strong magnet/ball materials, the acceleration would continue, but the balls would smash at a certain velocity. In fact, this is probably what would happen if you built a long enough train in real life - a shattered magnet would stop it long before it reached a steady state.

However, with respects to perpetual motion and the circle, after firing, the stage has expended its stored energy to accelerate the ball, and cannot fire again without you setting it back to the initial state (and thus expending energy to do so). Perpetual motion guys, energy's gotta come from somewhere! In this case - it's your hand.

[trebuchet03]

Not quite right. In a straight line,

Welcome to this thread... Allow me to introduce you to the subject:
What changes would need to be implemented to keep this going in a loop?

[Rectifier]

Aha, but I was actually replying to your comment, which claims, quote: "So eventually, the whole thing fizzles out - even in a straight line". Which it does not, unless you are referring to something in the loop system that I didn't quite read right.

[trebuchet03]

Ahh, gotcha... It's hard to remember what I was thinking over a year ago :p In any case, given perpetual motion lasts forever, we'll need a line of balls/magnets without finite bounds. We know, supplies for anything are finite... Which is pretty much why devices that claim perpetual motion involve some sort of commutation :p It does appear that I missed a few details in my explanation of my thoughts :p

[finfan7]

actually they aren't losing energy. the magnets are adding energy at each stage. the real reason you couldnt use it as a perpetual motion machine is that after the first trip around there is no ball to continue post impact. (assuming use of 2 ball and one magnet at each stage) if the ball isn't there to go onward the magnet absorbs the shock and transfers it to the ruler and stops the chain.

[trebuchet03]

while that is true - someone could argue an infinite amount of balls. If that were possible, the reaction would stop due to energy losses before getting to the nth ball -- the same goes for a huge amount of balls. ANYTIME you have a collision, it is not elastic as there is no such thing as a perfectly rigid material, this inefficiency is released as heat. For the sake of simplicity, many collisions can be considered elastic - such as pool balls. But in the case of perpetual motion, small bits add up over time which is the fundamental downfall of any perpetual motion device...

[PerfectlySquare]

Must be that "depressing, new-age" Second Law of Thermodynamics. "There is no process that, operating in a cycle, produces no other effect than the subtraction of a positive amount of heat from a reservoir and the production of an equal amount of work." So basically like Trebuchet said; as each of those collisions produces heat, a fractional percentage of the mechanical energy that produced it is lost as radiant energy being emitted out of the system. Entropy sucks...stupid hippies. :p

[James (pseudo-geek)]

there where 2 people that DID build a prepetual motion machine, and it DID give more energy out than was put in. one guy built it with magnets, one guy build it with hydraulics. I'll get those papers out someday and post them for u guys. scientists arent always right.

[JamesRPatrick]

So why is the world still relying on oil for energy and not building these perpetual motion machines? Perpetual motion could only happen in space, balaced evenly between all magnetic fields, where there's no air to cause resistance and loss of energy.

[trebuchet03]

where there's no air to cause resistance and loss of energy.

It's really not air causing resistance.... at least, it's not the biggest factor. It's the inelastic collision. The fact you hear sound means that the steel is vibrating. Vibration is a loss of power (pretty much turned into heat) :p

[JamesRPatrick]

I was thinking of like, a spinning wheel in space.

[JamesRPatrick]

What do you say about that, James?

[James (pseudo-geek)]

Theres too much money involved in the oil business right now. if that where to shut down, the worlds economy would crash. if you read stuff about people that built these machines, every one of them was told to stop by the government. Did you ever think that scientists just MIGHT be wrong when they say that its impossible? did you know that it used to be tought in schools, and was confirmed by SCIENTISTS that the earth was flat?

[_soapy_]

Erm... "Scientists" have known the earth was round for pretty much as long as there have been scientists. The ancient Greeks knew it! What you are thinking of is the "Dark Ages" when science was told what to say by religious men with swords. There is no conspiracy, though. f it were possible, someone would have stuck it on Instructables by now, since they would already have sold enough electric back to the local grid to retire wealthy.

[James (pseudo-geek)]

Do you realize how much money the oil companies are making, and that they don't want to lose that?

[_soapy_]

I pay £600 a month in diesel for my van. Fuel in the UK is near $8.50 US for a US gallon. It's scary. I'm currently looking at ways to enhance the fuel efficiency of cars and vans with some of the hydrogen kits that are on the market. Once I'm happy they aren't fake. If I can work out a good way to make 50p a year worth of electric to sell back to the grid, I'll do it. If you can show me a way to generate energy from magnets (or anything) that requires less energy in, I'll pay the start-up costs, and give you 90% of the profits and a 49% share. There is not a thing "big oil" could do about it. Major governments cannot stop important things like press reports of royals being on the front line, or rape videos getting on YouTube, so how could they suppress so perfectly an idea for something people actually desperately want?

[James (pseudo-geek)]

I dunno. theres no money in stopping those videos though, so that could be it. people are crazy about money, and it ticks me off.

[JamesRPatrick]

So why wouldn't you just keep using it and sell energy to neighbors? And to stop needing oil from other countries would b better for the U.S., at least, unless you're not from here.